Considering various factors, such as decorativeness, scratch resistance, processability and cost, those chosen as appropriate from materials such as resins and metals have been used for housings of electronic devices such as a mobile phone. The housings have been required not only the function of storing electronic components therein but also designabilities for tint of their colors, decoration thereof, and so on.
Of the designabilities, tints in particular are important factors.
In recent years, an attempt to use, as a material for housings, glass which had been not used has been made (Patent Document 1). According to Patent Document 1, the housing body formed from glass can produce effects of giving clarity, unique decoration on an electronic device such as a mobile phone.
Each of electronic devices has a display device such as a liquid crystal panel, on the outer surface thereof. Such a display device tends to become higher in definition and luminance, and with this tendency, backlight as a light source thereof also tends to become higher in luminance. Not only the display device side is radiated with light from the light source, but also there are cases where the light is repeatedly reflected inside the electronic device and reaches to the rear surface of an exterior housing.
Likewise, even in an organic EL (Electro-Luminescence) display requiring no light source, there is a concern about leakage of light from a light-emitting element. Although no problem is presented in the case of using metal as material for a housing, the above-cited case of using glass with clarity arouses a concern that light from a light source may pass through the housing and be recognized from the outside of the device. At the occasion of using glass for the housing, it has therefore been carried out to form a light-shielding means, such as a coating film, on the rear surface of the glass for the purpose of giving the housing the property of shielding from visible rays of light (hereinafter simply referred to as “shielding property”).
With luminance enhancement of a light source included in a display device, there arises necessity of having to form a thick coating film or form a film with a plurality of layers on the rear surface (on the device side) of glass in order to form a coating film having a sufficient shielding property, and this necessity becomes a factor behind increases in number of steps and cost.
In addition, when the coating film is not uniformly formed, light passes through only thin portions of the coating film and arouses a concern that visual beauty of the device may be impaired e.g. by shades of the housing being recognized as locally light. For example, in the case of a concave housing, it is necessary to form a uniform film on the entire surface of a concave surface side. However, a step of uniformly forming a coating film having a sufficient shielding property on the concave surface is complicated, and leads to an increase in cost.
At the occasion of obtaining a housing having a white appearance in particular, as mentioned above, it is possible to adopt a method of forming a white coating layer on at least one surface of a transparent glass. However, a white coating material has high transparency, and even though a thick layer thereof is formed, it cannot have a sufficient shielding property.
Accordingly, it is carried out to laminate a black coating layer having a high shielding property to a white coating layer. In this case, it becomes necessary to make the white coating layer thick enough to preclude the black coating layer from being perceived. Thus, the formation of a white-colored housing having a high shielding property through the use of a white coating material has a problem of involving very high cost.
Further, considering fracture by dropping shock during use or contact flaws resulting from long-term use, an electronic device usable as a mobile phone or the like requires its housing to have high strength. In order to enhance resistance of a glass substrate to flaws, glass has so far been chemically strengthened, thereby forming a compressive stress layer in the glass surface.
On the other hand, a gallery or a tunnel is high in temperature and humidity on the inside thereof and air therein is polluted, and hence its wall surface deteriorates fast. In addition, no daylight is shining on the inside of a gallery or a tunnel, and artificial lighting is therefore required during not only nighttime but also daytime. Great amounts of electric power are consumed by lighting of galleries and tunnels scattered throughout the country, and power savings have therefore been hastened.
As a material for the interior part of the gallery or tunnel, tiles with high reflectance have been used traditionally. The use of highly reflective tiles allows reduction in number of lighting fixtures, and it has yielded energy savings. In addition, visibility enhancement has been effected. As to the currently-used interior tiles for tunnels, application of coatings of glaze to their respective ceramic substrates has been carried out for the purpose of enhancing the ability to be cleaned, reflectance or strength.
For example, light-reflecting tiles for interior use of a tunnel have been described in Patent Document 2, wherein the tiles each has had a plurality of particulate asperities formed on a substrate surface thereof and the substrate surface has been coated with glaze for the purpose of increasing the strength thereof. Further in the document, the glaze rendered whitish by incorporation of zirconia into transparent glaze has been mentioned as a white glaze.
Furthermore, highly reflective white tiles to be used as a building material or wall material of buildings have been described in Patent Document 3, wherein there has been a description that contamination control treatment using glaze has been given to the tiles as required.